1. Field of the Invention
The present invention relates to an adaptive antenna reception apparatus. More particularly, the present invention relates to an adaptive antenna reception apparatus, which receives a CDMA (Code Division Multiple Access) signal as a multi-beam signal with adaptively controlled weights.
2. Description of the Related Art
A CDMA system has a possibility that a capacity of subscribers can be increased, and is expected as a radio access system of a mobile communication celler system. However, there is a problem that a signal from another user accessing at the same time functions as an interference signal in a base station receiving end. An adaptive array antenna reception apparatus is known as a method of receiving only a desired signal while removing the interference signals. The adaptive array antenna reception apparatus receives a signal by a plurality of antennas, carries out a weighting operation using complex numbers and a combining operation to control the amplitude and phase of the reception signal of each antenna and to form a directional beam for reception of a desired user signal, and for suppression of the other user interference signals.
FIG. 1 shows a circuit structure of a first conventional example of an adaptive antenna reception apparatus. Referring to FIG. 1, the first conventional example of the adaptive antenna reception apparatus is comprised of a path detecting section 200 and a receiving and demodulating section 100. A CDMA signal is received by an array antenna (not shown). A component of the CDMA received by each of antennas of the array antenna is referred to as an antenna-corresponding multiple spread signal hereinafter. The path detecting section 200 detects the timings of paths of the multi-path from the antenna-corresponding multiple spread signals. The receiving and demodulating section 100 carries out a despreading operation for each path to the antenna-corresponding multiple spread signals at the detected path timings, adaptively forms a directional beam signal for every path from the despread signals, and combines the directional beam signals to produce a demodulation signal.
The path detecting section 200 is comprised of a sliding correlation unit 201, a delay profile generating section 202, a delay profile combining section 203 and a path timing detecting section 204.
The sliding correlation unit 201 carries out the despreading operation to the antenna-corresponding spread signals over a plurality of chips in the resolution of 1/NR of a chip period (NR is a positive integer) and outputs sequences of despread signals. The delay profile generating section 202 vector-averages the sequences of despread signals for the respective antennas outputted from the sliding correlation units 201 in in-phase to calculate the signal level (amplitude or power), and carries out an averaging operation for an optionally predetermined time period. Thus, the antenna-corresponding delay profile generating section 202 produces antenna-corresponding delay profiles averaged for the predetermined time period for the respective antennas.
The delay profile combining section 203 combines the antenna-corresponding delay profiles to produce one delay profile. The path timing detecting section 204 detects a plurality of path timings from the delay profile and the path times are used in the receiving and demodulating section 100. The path timing detecting section 204 selects the timings of the paths with larger levels from the delay profile in order, while generally taking the path selection interval of 0.75- to 1-chip.
The receiving and demodulating section 100 is comprised of L (L is a positive integer) path reception sections (#1 to #L) 110-1 to 110-L for the number of paths of a multi-path, a combining unit 120, a decision unit 130, a switch 140, and a subtractor 150. The path (#1 to #L) receiving sections 110-1 to 110-L have the same structure and carry out the same operation. Therefore, the circuit structure and operation of the path (#i) receiving section 110-i (1≦i≦L) will be described. The path (#i) receiving section 110-i is comprised of a correlation unit 111-i, a beam former 112-i, a rake combining and weighting section 113-i, a normalizing section 114-i, a multiplier 115-i, and an antenna weight adaptive control section 116-i.
The correlation unit 111-i carries out a despreading operation to the antenna-corresponding spread signals at the path timings detected by the path timing detecting section 204. The beam former 112-i receives the outputs of the correlation unit 111-i with an antenna directionality by using antenna weights peculiar to the users and generated adaptively, and outputs a path-corresponding directional beam signal. The rake combining and weighting section 113-i carries out a weighting operation to the path-corresponding directional beam signal to correct a phase change. Also, the rake combining and weighting section 113-i carries out the weighting operation for SINR (desired signal power vs. interference noise power ratio) after the path combining to be maximized (maximum ratio combining).
The combining unit 120 adds the outputs of the rake combining and weighting sections 113-1 to 113-L for path combining and outputs a high quality demodulation signal. The decision unit 130 determines a transmission signal with a high transmission possibility from the demodulation signal. The switch 140 carries out a switching operation to use a known reference signal as a reference signal when there is the known reference signal and to use the output of the decision unit 130 as the reference signal when there is not any known reference signal. The subtractor 150 subtracts the demodulation signal from the reference signal and generates an error signal. The error signal generated by the subtractor 150 is distributed to the path (#1 to #L) receiving section 110-1 to 110-L, respectively.
The normalizing section 114-i carries out a normalization operation to channel estimation signal estimated by the rake combining and weighting section 113-i. Here, the normalizing section 114-i can be omitted to reduce a calculation quantity. The multiplier 115-i multiplies the error signal and the normalized channel estimation signal.
The antenna weight adaptive control section 116-i updates the antenna weights adaptively, by using the outputs of the correlation unit 111-i and the outputs of the multiplier 115-i. Minimum mean square error (MMSE) control is generally used in the antenna weight adaptive control section 116-i. In the MMSE control, the directionality is directed to the desired user signal and the control is carried out to maximize the SINR. As the adaptive update algorithm using the determination error signal, there are known LMS (Least Mean Square) algorithm and RLS (Recursive Least Square) algorithm.
In the first conventional example of the adaptive antenna reception apparatus shown in FIG. 1, the weighting and combining operation is carried out directly to the antenna-corresponding reception signals from the array antenna to from the directional beam signal. In this circuit structure, however, the beam formation is not carried out in the path detecting section 200. Therefore, the path detection cannot be carried out to utilize an antenna gain. Thus, there is a problem that the path detection characteristic is degraded when the number of antennas increases.
FIG. 2 shows the circuit structure of a second conventional example of the adaptive antenna reception apparatus as a multi-beam system. Referring to FIG. 2, the second conventional example of the adaptive antenna reception apparatus is comprised of a multi-beam former 301, a path detecting and beam selecting section 400 and a receiving and demodulating section 300.
The multi-beam former 301 receives antenna-corresponding multiple spread signals as a CDMA signal received by an array antenna (not shown) and outputs beam-corresponding spread signals as multi-beam signals. The path detecting and beam selecting section 400 receives the beam-corresponding spread signals and detects the timings of paths of multi-path while selecting one of the beam-corresponding spread signals in order. The receiving and demodulating section 300 selects one of the beam-corresponding spread signals, carries out a despreading operation to the selected beam-corresponding spread signal at the detected path timing to produce a path-corresponding signal, and carries out a weighting and combining operation to the path-corresponding signals for the paths to output a demodulation signal.
The multi-beam former 301 receives the antenna-corresponding spread signals as a multi-beam signal and outputs beam-corresponding spread signals for the respective beams. In order to reduce a calculation quantity in the multi-beam system, the multi-beam former 301 is generally arranged prior to the despreading operation for every user, and carries out a multi-beam reception operation to a multiple signal in which signals from all the users are multiplexed. With this, the calculation quantity per user can be greatly reduced.
The path detecting and beam selecting section 400 is comprised of a sliding correlation unit 401, a delay profile generating section 402, a path timing detecting section 403 and a path timing detecting section 404.
The sliding correlation unit 401 carries out a despreading operation to the beam-corresponding spread signals over a plurality of chips in the resolution of 1/NR (NR is a positive integer) of chip period, and outputs sequences of despread signals. The delay profile generating section 402 vector-averages the sequences of despread signals for the respective beams from the sliding correlation unit 401 in-phase, calculates the level (amplitude or power) of the signals, and carries out averages over an optionally predetermined time period. Thus, beam-corresponding delay profiles are obtained.
The path timing detecting section 403 detects a plurality of beam-corresponding path timings from the beam-corresponding delay profiles independently for every beam. The path timing detection is generally carried out to select timings of the paths with larger levels from the beams-corresponding delay profiles in order while taking the path selection interval of 0.75- to 1-chip. The path timing detecting section 404 collects the beam-corresponding path timings detected by the path timing detecting section 403, selects the timings of the paths with a plurality of larger levels from the collected beam-corresponding path timings and outputs sets of the selected path timing the beam number of the selected path timing.
The receiving and demodulating section 300 is comprised of L path (#1 to #L) receiving sections 310-1 to 310-L for the number of paths and a combining unit 320. The path (#1 to #L) receiving section 310-1 to 310-L have the same circuit structure and carry out the same operation. Therefore, the path receiving section 310-i (1≦i≦L) will be described. The path receiving section 310-i is comprised of a switch 311-i, a correlation unit 312-i, and a rake combining and weighting section 313-i.
The switch 311-i carries out a switching operation based on the beam number outputted from the beam/path timing detecting section 404 to select one from among the beam-corresponding spread signals. The correlation unit 312-i carries out a despreading operation to the selected spread signal at the path timing selected by the path timing detecting section 404.
The rake combining and weighting section 313-i carries out a weighting operation to the output of the correlation unit 311-i to correct a phase change. Also, the rake combining and weighting section 313-i carries out the weighting operation for SINR after the path combining so as to be maximized (maximum ratio combining). The combining unit 32 adds the outputs of the rake combining and weighting section 313-1 to 313-L for path combining and outputs a high quality demodulation signal.
In the adaptive antenna reception apparatuses of the circuit structure as described above, the path detecting and beam selection section 400 carries out the path detection using the beam-corresponding spread signals formed by the multi-beam former 301. Therefore, the path detection characteristic never degrades even when the number of antennas is larger.
However, in the first conventional example of the adaptive antenna reception apparatus shown in FIG. 1, the beam forming is not carried out in the path detecting section 200. Therefore, the path detection cannot be carried out to utilize an antenna gain. For this reason, the path detection characteristic degrades when the number of antennas becomes larger. Also, the path detecting section 200 cannot generate the initial antenna weights used in the beam formers 112-1 to 112-L of the receiving and demodulating section 100, at the same time as the path timing detection.
Also, the second conventional example of the adaptive antenna reception apparatus shown in FIG. 2 can solve the above-mentioned problem. In this structure, however, the receiving and demodulating section 300 processes the beam-corresponding spread signal selected from the outputs of the multi-beam former 301. Therefore, the adaptive beam forming cannot be achieved in which reception SINR is maximized, unlike the receiving and demodulating section 100 shown in FIG. 1 in which the antenna-corresponding signal is directly received.
In conjunction with the above description, an array antenna system of a radio base station is disclosed in Japanese Laid Open Patent application (JP-A-Heisei 11-266180). In the array antenna system of the radio base station for CDMA mobile, a beam former (12) carries out beam forming to a multi-path signal received by a plurality of antenna elements of the array antenna (11) to form a plurality of beams (B1 to B4), which are supplied to despreading/delay adjusting sections (finger sections) (131 to 13k) provided for the respective paths of the multi-path. Each of the finger sections carries out a despreading operation to a corresponding one of the plurality of beams. A beam selector (15) selects ones having larger signal components from among the despread signals for all the beams of all the paths. A combining section (17) combines the selected despread signals with weights, and a determining section (18) identifies data based on the combined signal. A searcher measures a time interval between the multi-path signals and supplies a despreading operation start timing and a delay time signal to the despreading/delay adjusting section provided every path of the multi-path.
Also, an adaptive array diversity receiver is disclosed in Japanese Laid Open Patent Application (JP-P2000-31874A). In this reference, a reception circuit phase-detects each of reception signals outputted from a plurality of antenna and outputs phase baseband signals according to the phases of the reception signals or time difference values between the phases of the reception signals. A phase error detecting section subtracts the phases of a half of ideal symbol points when there are no noise, interference, and distortion from the phase baseband signal, and outputs phase errors with sign to the half of the ideal symbol points. An absolute value calculating section outputs an absolute value of each of the phase errors with the sign as a phase error for each branch. A weight calculating section outputs weights according to each of the reception signals. A weighting section weights and adds the phase errors of the respective branches with the weights. A first combining section adds and combines the phase errors of the respective branches weighted by the weighting section, and outputs a first combined phase error to the half of the ideal symbol points for every point of the half of the ideal symbol points. A second combining section adds the weights, subtracts the first combining phase error from the weight, and outputs a second combining phase error to a remaining half of the ideal symbol points for every ideal symbol point of the remaining half. The remaining half of the ideal symbol points have the different phases from the half of the ideal symbol points by the phase of π radian. A determining section determines the ideal symbol points corresponding to the smallest one of the first and second combined phase errors, and outputs codes corresponding to the determined ideal symbol points as demodulation data. The weight calculating section updates the combined weights in accordance with the reception signal strength of each of the reception signals, the first or second combined phase errors of the ideal symbol points corresponding to the reference data, and each branch phase error of the ideal symbol points corresponding to the reference data. The reference data is known data contained in the demodulation data or a transmission signal from said determining section.
Also, an array antenna reception apparatus is disclosed in Japanese Laid Open Patent Application (JP-P2000-91833A). In this reference, the array antenna reception apparatus gives a signal received by a plurality of antenna elements provided in parallel an optional amplitude and a phase rotation to form a desired antenna pattern. An analog beam former inputs an output signal of each antenna element and combines beams such that the phase difference between the adjacent output beams shows a constant value which is decided depending on the selected output beams. A plurality of receivers change the respective output signals of the beam former into digital signals. A phase correcting section converts the digital signal into a digital signal which a phase correction quantity is given the output signal of each receiver such that the phase difference between the antenna elements is a constant value. The phase correcting section is comprised of a calculating section and a plurality of phase rotating sections. The calculating section multiplies digital signals between the adjacent beams, and subtracts the constant value from the multiplying result to determine the phase correction quantity, and adds the phase correction quantity to the phase correction quantity determined from the digital signal between the following adjacent beams. The plurality of phase rotating sections phase-rotate the digital signal by the phase correction quantity except for one as a reference.
Also, a path search circuit in a CDMA cellular system is disclosed in Japanese Laid Open Patent Application (JP-P2001-36451A). In this reference, the path search circuit is comprised of an antenna section of a plurality of elements. A plurality of radio receiving sections frequency-converts a radio Frequency signal received by each element of the antenna section into a baseband signal. An analog-to-digital converter converts each baseband signal into digital data. A plurality of correlation calculating sections calculate the mutual correlations of the baseband signals and known signals on the receiving end, and outputs correlation signals. A weighting average calculating section carries out a weighting and adding operation to the correlation signals outputted from the correlation calculating sections based on specified weighting coefficients and carries out an averaging operation for a predetermined number of times. A correlation peak detecting section detects one or more peaks from among the correlation signals after the weighting and averaging operation as a delay profile outputted from the weighting and averaging section, and outputs a reception timing and a reception level corresponding to the detected peak as the reception timing and the reception level of the reception path. A weighting control unit sets a directionality of the antenna section by controlling the weighting coefficients, and generates the plurality of weighting coefficients to form a plurality of antenna directionalities to divide a sector where a mobile terminal as a communication end is present.
Also, a CDMA adaptive receiving apparatus is disclosed in Japan patent No. 2,914,445. In this reference, the CDMA adaptive receiving apparatus is comprised of a set of the weighting and combining section and the weight control section for every user, and an error generating section. The weighting and combining section carries out a weighting and combining operation corresponding to the input of each of N antennas which receive a code division multiple access signal. The weight control section outputs antenna weighting coefficients for the weighting operation. The error generating section generates M error signals corresponding to the respective paths to desired signal from a channel estimation signal and M demodulation signals demodulated at timings corresponding to M paths of a multi-path from the reception signal outputted from the weighting and combining section, and combines the error signals to output to the weight control section.
Also, a diversity reception apparatus is disclosed in International Patent application WO97/20400. In the diversity reception apparatus of this reference, a correlation unit despreads a plurality of fading reception waves for every branch, when a data signal which has been transmitted in a direct CDMA system is received. A plurality of multipliers multiply despread signals and weight coefficients. The diversity reception apparatus is comprised of an identification section which reproduces the data signal, and a weight coefficient calculating section which uses an identification error signal which is obtained from an input signal to the identification section and an output from the identification section, as feedback data for controlling the weight coefficients.